A large variety of fifth wheel couplings are known in the patent literature and on the marketplace. Generally these comprise a plate having a rearward facing slot for receipt of a pin extending downwardly from a trailer, and a locking mechanism for automatically locking the trailer pin against removal once the pin is inserted a predetermined amount into the slot. The plate is usually provided with recesses to receive grease, which is manually applied.
Fifth wheel coupling devices should be of sturdy build, easy to couple and uncouple, and should hold securely the trailer in coupled position. However, practical experience has shown that conventional fifth wheel couplings require a significant amount of maintenance due to wear resulting in costly downtime for the vehicle operator. It is also known that under certain circumstances, the locking mechanism of the fifth wheel coupling fails, permitting disengagement of the trailer from the truck pulling it with disasterous results. An even more serious problem of conventional fifth wheel couplings is the lack of release mechanism in the event the trailer overturns. This means that the tractor pulling it is overturned with the trailer.